Multi-component Anti-extrusion Barrier for a Compression Set Subterranean Barrier

ABSTRACT

A backup ring assembly is disposed between opposed cones. The assembly rides up a wedge ring to contact a surrounding tubular when the opposed cones are pressed axially together to also compress the sealing element. The backup ring assembly has nested split rings that are slant cut for the split. The split for the nested rings can be circumferentially aligned or offset. Another ring is stacked axially adjacent the nested rings and has a slant cut for a split that is preferably rotated from the slant cuts of the nested rings. The interface of the nested rings can be along a line that is parallel to the mandrel axis or askew to the mandrel axis. The preferred material is a non-metallic composite material.

FIELD OF THE INVENTION

The field of the invention is backup ring assemblies that addresselement extrusion issues and more particularly designs involvingnon-metallic components for future milling out configured to radiallyextend without damage and without leaving extrusion openings.

BACKGROUND OF THE INVENTION

Packers and bridge plugs have sealing elements that are axiallycompressed to radially expand and seal off one part of a wellbore fromanother. The act of axial compression of the sealing element and thedifferential pressure when the set packer or bridge plug is in servicetends to force the sealing element to extrude axially. Barriers ofdifferent styles have been used in the past in various locations tocounteract this tendency to extrude. US Publication 2004/0036225 shows apair of axially stacked rings 270,280 that have a triangularcross-section and are pushed out radially together to control extrusion.US Application 2009/0255690 shows a combination of axially stackedslotted rings 72 working in conjunction with an adjacent 1-shaped backupring that is attached to an end of a sealing element. The slots areoffset in each row of the stack to prevent a barrier from opening up.U.S. Pat. No. 8,016,295 shows a helical backup ring that grows in radialdimension when axially compressed. It features tapered ends so that theends can sit flush to the adjacent structure. In US Publication2011/0036561 the extrusion barrier is a series of arcuate ring segmentsthat overlap at their ends so that as a slip ring made of wedge segmentsgrows in diameter the extrusion segments separate but continue tooverlap to close off any extrusion paths. US Publication 2010/0276137illustrates a vertically stacked end ring design with slots where theassembly is pushed out against the borehole wall by axial compression ofthe sealing element 14. The rings are taught to be made of a variety ofnon-metallic materials including composites. In other designs thesealing element itself has a fibrous layer internally next to a cablelayer to prevent seal element extrusion as described in U.S. Pat. No.7,510,015.

Some packers or bridge plugs are designed to be milled out at a latertime after they are set. To facilitate the milling out some of the partsare made of a soft material such as composite materials such as themandrel and the cones that compress the sealing element. In mostinstances the backup rings have been made of metallic materials out of aneed to give them the strength required to resist element extrusion.However, the use of metals for the backup rings also has an undesirableeffect of increasing the time to accomplish the milling out. On theother hand, use of non-metallic backup rings brings up service issuesthat have in the past kept such systems from being deployed. Thenon-metallic materials have more limited flexibility and can be subjectto snapping if they are flexed too much in any direction.

The present invention provides an assembly that serves as a backup ringthat is made from a non-metallic material preferably composites and usesa radial nesting of rings to minimize flexing of each ring as theirdiameter is increased when riding up a ramped ring adjacent the sealingelement. An adjacent ring axially abuts the radially nested rings withan offset cut so as to avoid opening extrusion barriers on radialgrowth. The nested rings are also slant cut to prolong the overlap astheir diameter grows. These and other features of the present inventionwill be more readily apparent from a review of the details of thepreferred embodiment and the associated drawings while recognizing thatthe full scope of the invention is to be determined by the appendedclaims.

SUMMARY OF THE INVENTION

A backup ring assembly is disposed between opposed cones. The assemblyrides up a wedge ring to contact a surrounding tubular when the opposedcones are pressed axially together to also compress the sealing element.The backup ring assembly has nested split rings that are slant cut forthe split. The split for the nested rings can be circumferentiallyaligned or offset. Another ring is stacked axially adjacent the nestedrings and has a slant cut for a split that is preferably rotated fromthe slant cuts of the nested rings. The interface of the nested ringscan be along a line that is parallel to the mandrel axis or askew to themandrel axis. The preferred material is a non-metallic compositematerial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a run in view of the backup ring assembly;

FIG. 2 is the view of FIG. 1 in the set position for the backup ringassembly;

FIG. 3 is an end view of one of the split rings showing the scarf cut;

FIG. 4 is the view along lines 4-4 of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 a packer P has a mandrel 10 with a center line 12that is inserted into a borehole 14 can be open or cased hole. A sealingelement 16 is flanked on opposed sides with wedge rings 18 and 20 thatare tapered to present opposed ramps 22 and 24 that are disposed inplanes that intersect the centerline 12. Cones 26 and 28 are broughttogether axially along the mandrel 10 in a manner known in the art toset the sealing element to the sealed position of FIG. 2. Such relativemovement of the cones 26 and 28 also brings the wedge rings 18 and 20closer together as they translate without rotation along the mandrel 10as can be seen by comparing FIGS. 1 and 2. The backup ring assemblies 30and 32 are disposed in mirror image orientation on the ramps 22 and 24respectively.

Each of the assemblies 30 and 32 comprise at least three rings 34, 36and 38. Rings 34 and 36 are nested and are preferably concentricallydisposed about the mandrel 10. Surfaces 39 and 40 respectively on rings34 and 36 are flush against an adjacent cone such as 26 or 28. Ring 38is preferably trapezoidal in section and has a side 42 that sits upagainst surfaces 44 and 46 of adjacent rings 34 and 36. Rings 34 and 38have sloping sides 48 and 50 that ride on surfaces 22 or 24 of the wedgerings 18 or 20. Rings 36 can also have an undercut 52 or 54 that raisesoff the mandrel 10 in the run in condition or those surfaces can beflush with the mandrel 10 for run in as another option.

In section, ring 34 is preferably a rectangle but can be a square or atrapezoid, for example. Ring 36 in section can be a quadrilateral butcan have other shapes. These two shapes preferably have a side in commonsuch as surfaces 56 and 58 and in section the line that represents theircontact can be oriented parallel to axis 12 as shown or at a skew tothat axis. Preferably rings 34 and 38 have contact surfaces 60 and 62that that are oriented flush to the borehole 14 and generally parallelto the axis 12.

FIG. 3 shows the cut that is preferably in each of the rings 34, 36 and38 but is illustratively shown for ring 34. The split 64 is a scarf cutalong a plane that intersects the axis 12 so that sliding ends 66 and 68can move relative to each other while remaining in contact and withoutopening up a gap. The cut 64 in rings 34 and 36 that are radially oneoutside the other can be circumferentially aligned or offset. From theperspective of the sealing element 16 putting the cut 64 of the ring 38at a circumferentially offset location from the split 64 in the ringpair 34 and 36 prevents an extrusion gap from opening. The stackingradially of the rings 34 and 36 reduces the amount of radial deflectionthat each has to have to reach the borehole wall 14. The location of thenested rings 34 and 36 between a cone such as 26 and ring 38 as theyride together along sloping ramp 22 until surfaces 60 and 62 contact theborehole 14 provide structural support to the nested rings 34 and 36 tokeep them from twisting or separating at the cut 64. Surfaces 60 and 62do not need to engage the borehole 14 at the same time but that is onepossibility. If surface 60 engages first the presence of the ramp 22 or24 will aid the adjacent surface 62 to continue outward movement untilcontact is made with the borehole 14. Similarly engagement of assembly30 to the borehole 14 can occur before assembly 32 makes contact but aslong as setting pressure continues to be applied the assembly on theother side of seal 16 will make contact with the borehole 14.

As shown in FIG. 4 the rings 34, 36 and 38 have a height h that extendsin a radial direction from mandrel 10 to an end 74 and between adjacentstraight sides 70 and 72 that are preferably in parallel planes but canbe converging or diverging as alternative designs. In essence the ringsare discs with an open interior to fit either around the mandrel 10 asin the case of rings 36 and 38 or against another ring such as ring 34having an opening that rests on ring 36.

Preferably the assemblies 30 and 32 should be made from a drillable softmaterial such as the preferred material which is a composite.

Those skilled in the art will appreciate that a non-metallic backup ringassembly is provided that is less stressed due to the reduced radialgrowth brought about by nesting two or more rings in one row that isabutted by another ring in an adjacent row to provide lateral stabilityin the set position. The rings are slant cut with the abutting ring tothe nested rings having a circumferentially offset slant cut from eitherof the nested rings whose slant cuts can be aligned or offset. While asingle row of nested rings that are preferably coaxial is describedadditional rows of nested rings can be used if there is space dependingon the size of the packer. Another option is to sandwich a row of nestedrings between single rings on opposed sides with at least some of therings having a split cut at a slant. The cut angle can vary with respectto the axis 12 in a range of 25-75 degrees. The material for all therings can be identical or alternatively the materials can be differentwhile all preferably are non-metallics.

The above description is illustrative of the preferred embodiment andmany modifications may be made by those skilled in the art withoutdeparting from the invention whose scope is to be determined from theliteral and equivalent scope of the claims below:

I claim:
 1. An extrusion barrier assembly for a compression set sealingelement that selectively isolates one subterranean location fromanother, comprising: a sealing element mounted on a mandrel; an axiallymovable compressing assembly for said sealing element mounted on saidmandrel; said extrusion barrier comprising at least one row of radiallynested rings mounted over said mandrel, said rings extending in a radialdirection from said mandrel to an end between straight sides and atleast a portion of said rings are driven away from said mandrel by saidcompressing assembly.
 2. The assembly of claim 1, wherein: said ringsare split to define adjacent ends.
 3. The assembly of claim 1, wherein:said split is in a plane that is skewed to an axis of said mandrel. 4.The assembly of claim 2, wherein: said splits are circumferentiallyaligned.
 5. The assembly of claim 2, wherein: said splits arecircumferentially offset.
 6. The assembly of claim 2, wherein: said endsoverlap each other after said compressing assembly drives said nestedrings.
 7. The assembly of claim 1, wherein: said rings are made of anon-metallic material.
 8. The assembly of claim 7, wherein: said ringsare made of a composite material.
 9. The assembly of claim 2, furthercomprising: an additional row with at least one additional ring adjacentsaid nested rings.
 10. The assembly of claim 9, wherein: said additionalring is split to define adjacent ends.
 11. The assembly of claim 10,wherein: said split in said additional ring is circumferentially offsetfrom said split in said nested rings.
 12. The assembly of claim 11,wherein: said ends of said additional ring overlap each other after saidcompressing assembly drives said nested rings.
 13. The assembly of claim12, wherein: said additional ring is made of a non-metallic material.14. The assembly of claim 13, wherein: said additional ring is made of acomposite material.
 15. The assembly of claim 2, further comprising: atleast one wedge ring between said sealing element and said extrusionbarrier that presents a ramp for said extrusion barrier as saidextrusion barrier is moved away from said mandrel by said compressingassembly.
 16. The assembly of claim 15, wherein: said split is in aplane that is skewed to an axis of said mandrel.
 17. The assembly ofclaim 16, wherein: said ends overlap each other after said compressingassembly drives said nested rings.
 18. The assembly of claim 17,wherein: said rings are made of a non-metallic material.
 19. Theassembly of claim 18, further comprising: an additional row with atleast one additional ring adjacent said nested rings. said additionalring is split to define adjacent ends; said ends of said additional ringoverlap each other after said compressing assembly drives said nestedrings.
 20. The assembly of claim 19, wherein: said split in saidadditional ring is circumferentially offset from said split in saidnested rings. said additional ring is made of a non-metallic material.